In land-mobile radio dispatch, there is the need for controlling a radio base station with a user-friendly device that is specific to the operating environment. Several methods for controlling a radio base station exist today with each having different limitations. These methods are described below after the following description of how a ratio base station generally operates.
FIG. 5 illustrates a block diagram of a conventional radio base station known to those skilled in the art of the invention. Radio base station 500 refers collectively to all the components shown in FIG. 5, which include a transceiver tower 502, a radio 504 (e.g., which comprises power transmission amplifiers, modulating and demodulating circuits, interface and power-control circuits, among others), an adapter 506, a local dispatch device (LDD) 510, and one or more remote dispatch devices (RDDs) 508a-508d. The operation of radio base station 500 is well known to those skilled in the art, but its salient features are mentioned herein as an aid in understanding the discussion below. Radio 504 transmits a modulated signal to transceiver tower 502, which then transmits a radio frequency signal to one or more distant transceivers (not shown). These distant transceivers can be used by police, fire, rescue, military or security personnel for which centralized communications is necessary or desired, or by assistants on a ranch, or by employees of a large industrial manufacturing or warehouse facility, among other uses. Regardless of the operating environment, it is be desirable and/or necessary to maintain two-way communication capability with the associated individuals. These associated individuals have two-way communication devices (i.e., transceivers) that can receive signals from and transmit to the transceiver tower 502 and radio 504.
Adapter 506 allows more than one dispatcher (i.e., a person who talks to the distantly located individuals with transceivers) to communicate over radio 504 and transceiver tower 502 to these individuals. Adapter 506 can control radio 504 based on commands received from a LDD 510, which can be co-located with the adapter 506, and RDDs 508a-508d. Adapter 506 receives the commands generated by the RDDs 508a-508d and/or LDD 510, prioritizes them, and translates them into signals that are understood by radio 504. Adapter 506 receives audio signals from RDDs 508a-508d and/or LDD 510 and sends them to radio 504, which modulates a carrier frequency (AM, FM, FSK, PSK, and so on) to transmit the audio signal on a desired frequency (or channel) to the distant transceivers.
When an RDD 508b controls the radio base station 500, it sends signals that directs the adapter 506 in its operation. The adapter 506 controls the radio 504 which, in turn, controls the transceiver tower 502. However, adapter 506 can also control RDDs 508a, 508c and 508d based on what RDD 508b has directed it to do. This is because, even in a typical “feature-less” radio base stations, transmitting on any one channel prevents other RDDs from transmitting on that same channel at the same time, even without bi-directional control signals, thereby controlling the entire radio base station.
In order of complexity, the methods of controlling a radio base station include: (1) local control; (2) direct current (DC) remote-control; (3) tone remote-control; and (4) digital control. Local control is characterized as a low cost, low functionality, direct connection between a controlling device such as a dispatch device and a radio using analog control information (i.e., analog signals) to control the radio. This system would not include an adapter, although the dispatch device can be several hundred feet from the radio. DC remote-control is characterized as more costly than methods (1) and (3), and provides more features than local control, but has limitations in functionality and in the type of circuit used to connect the controlling device to the radio. Tone remote-control is also characterized as more costly than method (1) but provides the most functionality and has the fewest limitations of the four methods of radio base station control. Tone remote-control is of interest in this environment due to its relatively high-level functionality, including parallel updating of multiple dispatch points and its ability to effectively provide control from remote locations (that might be many miles away) using a leased-line PSTN circuit.
In many applications, there is a need to control the radio base station from a remote location. For example, a typical radio dispatch environment might have a dispatch device located on the first floor of a tall building and a radio located on the roof. In this situation, local control may not be feasible due to the typical 1000-foot distance limitation of transmitting analog control information over copper wire and the size of the cable required to make the necessary connection. Furthermore, DC remote-control may prove insufficient due to its low level of functionality or the type of circuit available for the remote connection. For example, DC remote-control only supports four (4) channels of channel change (i.e., DC remote control is only capable of selecting 1 of 4 total number of channels), requires a DC continuous line between the dispatch device and the adapter (if there is one) or radio (which is currently, and for the foreseeable future, unavailable over leased PSTN lines), and cannot support parallel status updating among plural dispatch devices. Digital remote-control is a possibility, but it is expensive and requires sophisticated equipment.
In remote-control of a radio base station, several features are desirable. These include the following:                Activation of the radio transmit or push-to-talk (PTT) switch from a remote location;        Reception of the radio's receive audio;        Placing the radio in a monitor mode;        Changing the channel the base station is using; and        Dispatch awareness of the current state of the radio.        
Most of these are features available to DC remote-control and tone remote-control. Local control does not support channel change. One additional feature of tone remote-control that usually makes it desirable over both DC remote-control and local control is the ability for parallel dispatch points to be updated to the current setting of the radio.
In many situations, a base station may have several dispatch points connected to it. These dispatch points are not necessarily co-located. For example, through the use of leased PSTN lines, a first dispatch point might be located in a campus security building, while a second dispatch point might be located in the campus administrative office building. If each dispatch point has parallel status update capability, changing the channel of the base station at a first dispatch point will change the current channel-in-use indication at other dispatch locations. This is an important feature that provides the dispatcher the assurance that the base station is in a known state. Without parallel status updating, a dispatcher may think the radio is on one channel when, in fact, it is on another.
Tone remote-control uses standard tones for both control and carrier signals. Control tones are used to change the radio channel, put the radio in monitor mode and activate the radio PTT. A carrier tone superimposed on the transmit-audio is used to keep the radio PTT activated for the duration of the dispatcher's transmission. These tones are superimposed on the audio so that only one pair of wires is required from the dispatch device (i.e., as opposed to two pairs if one pair were dedicated to audio and the other is for control signals) and the tone remote-control adapter. In some applications, these same tones are detected and decoded by parallel dispatch devices to provide parallel status updating.
Some radios are designed to scan the RF channels that are programmed into it. This allows a single radio to scan several RF frequencies that could be used in an application. If the radio detects a carrier signal on one of the channels, it typically stops and displays the selected channel. Depending on the radio's capabilities, it might only display a numeric indication (e.g., an LED associated with an F1, F2, F3 or F4 button) to indicate the selected channel. Other types of radios use an alias, for example, “FIRE” or “POLICE” on an LED. If a carrier signal has not been detected, the radio scans to the next channel and so on, until the end of the channel list is reached. The radio then scans the first channel on the channel list, and so on. There are several variations with regard to scanning. For example, some radios provide priority scanning and other features, but the basic operation is the same. There is a deficiency in many scanning radios in that they cannot provide the scanned channel information to an external device.
The ability to scan the RF channels in a conventional radio is an important feature. Many conventional radios (as opposed to trunk radios or scanning radios, which, by definition, must have scanning capabilities) do not have scanning capabilities. These conventional radios instead use an external device to change the channel of the radio to monitor different RF channels. While the external device tunes the radio to a specific channel, all other channel activity will be ignored until those channels are selected. Further, the cost of a system design that supports simultaneous monitoring of multiple channels may be prohibitive and is reflected in the cost of the dispatch device, the number of remote adapters required, the number of radios required and the installation of such a system. These non-scanning conventional radios would clearly benefit from a remote adapter to facilitate external scanning control.
Currently, several manufacturers provide tone remote-control devices and adapters that allow the radio channel to be changed from a distant location. Further, several conventional radio manufacturers provide radios that include the ability for external control of the radio's channel. Nevertheless, all of these conventional tone remote-control devices are unable to provide current channel-in-use information to a remote dispatch device.
Therefore, a need exists for a device that can provide remote control of a conventional radio using tone remote-control which can provide current channel-in-use information to one or more remote dispatch devices.